


Open Season

by crowbeau



Series: Newlyweds Disregard the War for the Sake of Love [1]
Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: F/M, Mating Cycles/In Heat, Mentions of Breeding, Post-Coital Cuddling, Vaginal Sex
Language: English
Status: Completed
Published: 2019-08-29
Updated: 2019-08-29
Packaged: 2020-09-29 00:11:51
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 1
Words: 8,483
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20434817
Author URL: https://archiveofourown.org/users/crowbeau/pseuds/crowbeau
Summary: Seteth overhears a conversation between Byleth and Hanneman. He becomes increasingly worried for Byleth and makes a heated discovery about her current situation. Feeling connected by this innate burden that they both share, Seteth offers to help Byleth. (Contains spoilers for Seteth's identity and past).





	Open Season

**Author's Note:**

> y'all know im big on fe dragons so obviously,,, byleth and seteth,,, i mean,,, c'mon, man,,,,
> 
> (uh and, it doesn't really matter but my byleth is on the BL route,,, its brought up like Once at the end but, just in case,,, here's your warning,,, i never know!)

There was commotion in the hall as Seteth finished up the last few lines of his most recent fable. He tended to ignore the majority of hall squabbles, having grown accustomed to Manuela’s routine outbursts aimed at a certain Crest scholar. But this time, Seteth found himself listening in as he heard the undeniable lilt of the professor’s voice.

“_Hanneman_-,” Byleth gasped, “I need-, I can’t-,”

At the sound of her strained tone, a shiver skirted up Seteth’s spine and he got to a quick stand, startled. Around the monastery, Byleth was notorious for emoting very little. To hear her speaking as she did now-,

“This development must be documented at once, Professor!” Hanneman was saying, his eagerness overpowering his sense of reason.

It was typical. Seteth himself had managed to avoid most of the scholar’s attention—and kept Flayn from any major interaction—but Byleth was not so lucky.

“You must tell me everything that you’re feeling! If this is related to your Crest, it may be the key to unlocking the truth behind the Crest of Flames!” Hanneman continued, enthused.

Byleth let out a low sound. They must’ve been right on the other side of Seteth’s door now. Goddess, she sounded so close. And making a noise like that-!

“I can’t-, go any further,” Byleth ground out.

On the surface, she sounded annoyed. But Seteth had spent enough time studying her, initially expecting a betrayal of Rhea’s seemingly unfounded trust. He knew the truth of things: she was frightened.

“Wait there then, Professor,” Hanneman said, unaware of Byleth’s fear, “I’ll grab my quill and we’ll record things here.”

“Hanneman-,” she tried again.

But the scholar was already ducking into his office, scrambling around for suitable pen and paper.

Byleth must’ve sunken to the floor, her weight levying against Seteth’s door enough to have him leaping back from it like a startled cat. She let out another sound that could only be labelled as a moan.

“_Hanneman_-, I-,”

As the seconds ticked by, Seteth began to worry his teeth into his lower lip. It was not unlike him to stand by and let the two of them go about their study of the Crest of Flames, but-,

But something was wrong here. Byleth didn’t seem herself.

Seteth pulled open his door.

The professor tumbled back, clicking her tongue as she struck the back of her head on the flooring of Seteth’s office; her noise was the only evidence she’d been troubled by the motion. Seteth eased to his knees beside her, pulling Byleth into a sitting position against him.

Her head lolled back as though the weight of it was too much for the professor to bother trying to keep up. Her hazy gaze drifted, unfocused, until she blinked slowly.

“Set-, Seteth-?” she rasped, as though she thought him an illusion.

“Professor,” he murmured, “what’s happened to you?”

Instead of offering an answer, Byleth let her head rest against the adviser’s chest. She inhaled his gentle scent slowly, parting her lips as though that would amplify the aroma.

“You smell like-, the sea,” she whispered, “it’s-, good. Calming.”

She closed her eyes and though her comment had been uncharacteristically forward, Seteth felt relieved that she appeared to have relaxed.

“Professor-?” Hanneman’s voice bounced down the hall and Seteth hurriedly pulled Byleth further into his office before closing the door with the toe of his boot.

He swept Byleth up into his arms and she lifted her hands, wrapping them around his shoulders as though it were the most natural thing in the world. The professor pressed closer to him, exhaling a warm breath against the edge of Seteth’s collar; the sensation was enough to raise gooseflesh beneath his robes.

“You’re truly not yourself this evening, Professor,” Seteth murmured, taken aback by her uncharacteristic openness.

The rumble of Seteth’s voice in his chest made Byleth hum, pleased, and she nosed her way beneath the soft curl of his dark hair.

“I feel at ease with you,” she breathed against his jawline, perhaps by way of explanation.

The slight brush of her lips against his skin made Seteth shudder; it had been far too long since he-,

“I wonder why that is-,” the professor mused, “are you someone special to me, Seteth?”

For a long moment, Seteth had half-expected her to call him by his true name. It wasn’t disappointing, necessarily, when she did not.

“Seteth-?”

Hanneman’s voice came from just beyond the door. 

The adviser eased Byleth down into his desk chair before turning back to the door. What could he say? Though the professor had relaxed, Seteth felt the need to protect her well up within him, the weight of it nearly suffocating. It reminded him of the times when Hanneman had initially shown interest in Flayn. 

Seteth dropped his gaze to Byleth, considering; would she be angry if he stepped in? Clearly she and Hanneman had decided sink some time into studying the Crest of Flames, but in this state-,

Arms akimbo and sitting prone in the adviser’s chair, Byleth seemed uncharacteristically soft. Defenceless. When Seteth went to step away from her, the professor caught the edge of his wide sleeve in her hand.

“Professor-?”

“Don’t go,” she rasped, “the heat will come back and I’ll lose my mind-,”

Seteth stared at her.

“The-, the heat-?”

Byleth jerked her head in a crooked nod, “It comes in waves, roars in my ears-, please, Seteth, I can hardly think-!”

The reality of what she was describing hit Seteth like a ton of bricks and he whipped around to stare at the calendar.

“Is it possible-?” he wondered to himself.

“Seteth-?”

Hanneman again. The adviser knelt beside Byleth, taking her hand in his own. It was so small; had she always been so much smaller than him?

“Professor,” he said quietly, “I’m going to stay with you. I promise I will not leave you until this passes. But I must ask Hanneman to go.”

“He wants to do research,” Byleth murmured, straightening as though to stand, “I promised to help-,”

“You’re in no state to do such a thing. The studies can wait,” Seteth interrupted, tone sharper than he’d intended as he put a heavy hand to her shoulder.

Byleth growled at him, seeming less enthused to simply sit and wait, not that Seteth could blame her. He understood how she felt, truly, but now surely wasn’t the time to be getting up in arms about such trivial matters-,

“The students-,” Byleth hissed, shoving past him, “I can’t just leave them-, there are exams to be done tonight-,”

Seteth took her by the arm, the movement rougher than he intended and the professor whirled to face him, light gaze blazing.

“_Seteth-,_” she ground out, “release me.”

“_Byleth_,” he returned with a heavy-handed sternness generally reserved for defilers, “I’m telling you, you mustn’t continue on as though nothing is wrong-,”

“And _I’m _telling _you_ that I have a duty to my students! To Hanneman! To the _Church_!” she snapped, wrenching free and spinning on heel to stalk towards the door.

Seteth sighed, irritation and worry mixing in his chest like a mead with far too much kick. He matched her pace and caught Byleth by the hand, yanking her back towards himself.

“Professor,” he said, his voice low—if they spoke louder, surely Hanneman would hear and that would create an entirely _new_ problem—“I must insist-,”

Byleth made another attempt to pull herself free and Seteth pressed her back into the corner of his office before he knew what he was doing. When he glanced down, his hands were gripping at her slender wrists, pinning her back against the warped wood of the wall.

“_Seteth_-,”

“This needs to be dealt with,” the adviser whispered heatedly as he dropped his hands, “it is not something to be ignored until it dies down. Ignore it once and it’ll come back twice as fierce, Professor.”

Seteth closed his eyes, lifting his arms to bunch his hands in the fabric at Byleth’s shoulders as he tried to regain control over himself.

“I-, worry,” he allowed softly.

It ached to admit, to allow that fragile weakness back into his heart, yet again—was he simply the world’s biggest fool?—but here it was, having quietly made a home within him.

At the realisation that this care—something dangerously close to _love_—for Byleth had risen up inside him, Seteth opened his eyes and raised his head, looking into her face.

Byleth’s cheeks were stained with blush, her eyes half-lidded as she gazed at him.

“Set-Seteth-,” she murmured, and she was panting, chest rising and falling rapidly as she attempted to fight off the next wave of need, “I-, I want-,”

“I know-,” he returned, moving his hand to gently cup her face.

Byleth tipped her head, the movement almost imperceptive as she nestled into the warmth of his palm. She closed her eyes with a tired sigh.

“I know you’re frightened,” Seteth said, “and that is a natural thing. I can help you, if you’ll have me. But first, I must explain things to Hanneman.”

“I’m sorry, I-, snapped at you,” Byleth rasped, “that-, _this_-, is unlike me.”

Seteth ducked to press a feather-light kiss to the professor’s forehead before turning towards the door.

“Wait for me,” he breathed.

Hanneman met him in the hall.

“Seteth!” he greeted, warm as always—so damn eager to please and poke and _prod_ as always—“Have you seen the professor? We were just-,”

“Hanneman.”

“Yes-?”

Seteth reached up to tuck his hair behind his ear, suddenly apprehensive. But he caught himself before he could complete the motion; revealing his ears would likely only complicate things more.

He settled for clearing his throat instead as he folded his hands behind his back.

“The professor’s-, _symptoms_-, are in part, due to her birth,” he said, which wasn’t necessarily a lie, “and have little to do with her Crest.”

Hanneman scrutinised him for a long moment. Seteth wondered just how much the scholar had heard of his squabble with Byleth.

“It would be-, most beneficial for _me_ to be the one to-, assist her,” Seteth finally said, and the words were heavy on his tongue—the half-confession enough to warm his cheeks, “but if you must have the details, I will-, be willing to share them with you. At a later date.”

Hanneman considered this offer. 

Seteth wanted to return to his office, take up the Spear of Assal, and return to beat Hanneman over the head with it for taking such time to make his decision. The longer they stood there, the longer Byleth had to suffer alone.

The thought of it made some long-forgotten ache wake in Seteth’s chest. He closed his eyes, imploring the Goddess to spare some patience.

“That is acceptable,” Hanneman finally allowed.

Seteth hoped he was not visibly overjoyed by the news. 

He cleared his throat again and gave the scholar a curt nod.

“Thank you.”

Without waiting for a response, Seteth turned on heel and re-entered his office, closing the door without regard for appearing rude.

Hanneman put a hand to his chin as he paced back into his own office, thinking over the adviser’s words.

“Professor-,” Seteth whispered, kneeling beside where she’d sunken to the ground in the corner.

Byleth shifted, cracking open one eye to take in the sight of him.

“Seteth,” she breathed, and there was a hint of relief in her tone, “it’s you.”

“Yes. Now, I know this-, this may be difficult to hear, but I must explain things to you before things gets any worse. I want-, I want you to understand what’s happening while you still have your wits about you.”

He tried to keep his voice low, controlled. It wouldn’t do to frighten her further.

Seteth took the professor’s hand. Had he ever explained this before? Yes, once. But that had been-, oh, ages ago, now. Before he could dredge up the aching memory, Byleth spoke.

“I already know,” she murmured, oddly resigned, “I began to read up on things in the library, when it-, when this first started.”

“You-,”

“I know,” the professor repeated tiredly, “I have to mate.”

Seteth stared at her, unsure of what to say. He hadn’t expected her to know what was going on. But, even more jarring, was the fact that Byleth knew of her situation and yet had still agreed to cooperate with Hanneman.

“Did you truly think he’d spare you in a moment of weakness?” Seteth wondered, suddenly irritated.

Byleth blinked and focused on him, taken aback by his sharp tone.

“I-,”

“If he knew-,” Seteth whispered, and his voice shook, “if he knew you were _ripe_ for a _mate_, what makes you think he wouldn’t round up as many Crest-bearers as he could find? Knowing that you’re desperate-, that you _must_ mate regardless of your own thoughts on the matter-, don’t you see-? This would be-, what would he say? A ‘perfect opportunity’ to investigate the union of two Crest-bearers! How many experiments, Byleth? How many times would you be pried open until you would realise-?!”

Byleth stared at him, unblinking as she slowly took in his words. When she registered Seteth’s meaning, she went red in the face, angry and ashamed.

“That’s-! What are you _talking_ about, Seteth-?! That makes it sound as though Hanneman would make me-, have me act as some sort of-,”

She wrinkled her nose as she searched for the word.

“Breeder,” Seteth provided quietly, “yes.”

“Hanneman is not my enemy-, and even if he were, he would never-!”

Seteth gripped the professor’s hand so hard that her knuckles popped.

“_Byleth_-!” he hissed, and there was a fire in his eyes that she had not often seen outside the battlefield, “Our blood is precious. Our _bodies _are precious! You are-, like family to me, Professor. If something-, if something were to happen to you over this, I-,”

He trailed off, closing his eyes again. For a moment, he looked much older, much more tired, as though he was exhausted with life itself. Maybe he was.

“You-, _you_ are precious to me,” Seteth finally whispered, and when he opened his eyes, his expression was that of a wounded animal.

“Please, do not so easily submit yourself to such things when you are like this. I do not want you hurt. I do not want to see you in any more pain, ever again.”

They were both quiet for a long while as Byleth took in this information. She opened her mouth to say something but closed it without a word, seeming to think better of her comment.

“Seteth,” she said instead, after a moment’s reconsideration, “did you mean what you said before?”

The adviser blinked at her, uncomprehending.

“You offered to help me through this,” Byleth reminded, “were you-, offering to mate with me?”

Seteth pinked and his pointed ears twitched enough to poke out from beneath his curtain of dark hair.

“I-, I would have explained things in detail, first-, I have no intention of misleading you, especially in regards to something as intimate as-,”

“Seteth.”

The adviser trailed off, lifting his gaze to Byleth’s.

“Help me up,” she whispered, though there was no harsh command in her voice, “we should go-, to my chamber.”

“Mine is closer,” Seteth breathed as he gently pulled the professor to a stand.

Byleth was shaking, fists clenched up in the adviser’s robes until her knuckles went white, as though Seteth was her anchor. Perhaps that was how she saw things. 

Something about such a tender thought warmed Seteth’s heart.

He shook his head; now wasn’t the time to think such things, not when Byleth was in such a state.

“Professor,” he murmured, “if there is someone else-, if you’d rather-,”

“Seteth,” she said again, looking up into his face, “for being adviser to the Archbishop, you’re certainly dense.”

He blinked.

“I-,”

The rest of his sentence melted on his tongue as Byleth pushed up onto her tiptoes and pressed her lips to his. Seteth stared at her as her eyes fluttered closed. The professor wasted no time urging Seteth to deepen the kiss with a brush of her tongue against his bottom lip.

Want skittered through Seteth like an electrical current as Byleth gasped into his mouth, drawing back only to nose her way against his neck. She pressed a quick kiss to his jawline and then another, slipping down just above his pulse. Seteth tipped his head to the side on reflex, eager for more of her attention despite himself.

When Byleth lifted a hand and struggled with the buttons at his collar, the adviser put his hand to hers, stilling the motion.

“Professor,” Seteth said, and his voice was gruff as he tried to regain some self-control, “please have patience. We’re not far from my chamber.”

“Rather than discuss it, let’s go-,” Byleth hissed desperately.

Seteth took her hand in his own, gave it a squeeze, and then helped her into the corridor.

***

Seteth had scarcely closed the door before Byleth was upon him, hands wandering across the wide expanse of his chest as she pinned him back against the rough wood of the door. Despite the thick fabric of his robes, Seteth felt the professor’s touch like a kiss of flame. 

And though he wasn’t driven by his own quaking need, Byleth’s heat was practically contagious, sinking into him with each cautious caress.

“_Professor_-,” Seteth murmured and he scarcely recognised his own voice, startled by the weakness he found there, “we-,”

“There’s no time,” she interrupted, “I’ve waited-, for so long.”

When Byleth put her nose back to his neck, inhaling his sea-scent, Seteth couldn’t help but sigh, contented; something about participating in such a ritual—one so close to his heart and so innate for his kind—was oddly freeing. 

And for just this moment, lost in time, he felt utterly weightless.

“Why did you wait-?” Seteth wondered, more to himself than to Byleth.

Why had either of them waited? If Seteth had known it was going to be like this, he-,

“Isolation,” Byleth said by way of explanation, her breath hot against Seteth’s jawline, “inexperience. An innate fear of rejection.”

Perhaps it was true for the both of them.

“Byleth-,” Seteth whispered, embracing her suddenly.

He held the professor to his chest, her head of minty hair tucked beneath his chin. He ran a hand up and down her back, the motion soothing her mounting tension.

“I never meant to make you feel that way.”

“I know,” said Byleth, “but it doesn’t matter now.”

“Because you want to mate?”

Byleth laughed against his chest and the sound was such a rare one that in the moment, Seteth nearly forgot to breathe.

“With you, Seteth. Yes.”

He nodded slowly, still recovering from that jingling sound she’d produced; how had he resisted such gentle charm before now? With the professor pressed against him, relishing his soft sea scent, Seteth lifted his hand and ran it through her hair.

Byleth hummed appreciatively, seeming pleased with his careful touches.

“You’re certain of this?” Seteth asked as he released her, dropping his hands to take Byleth’s own as he guided her towards the bed.

She nodded, in quiet contemplation as Seteth turned to look back at her for some confirmation.

“I-, care for you. And for Flayn,” Byleth said, and her words were so soft that the adviser had nearly missed her comment altogether, “she was-, so delighted when I finally caught The Fish, you know.”

The professor trailed off and Seteth could only stare at her, hopelessly starstruck as a soft smile slowly spread across Byleth’s face as she recalled the memory.

She looked radiant. 

When she lifted her gaze to meet Seteth’s, he felt embarrassment flood his cheeks, certain the professor had seen all the love in his expression in that moment.

Byleth’s gaze softened and she cupped the adviser’s face, thumbing his cheeks gently. And then she went to tuck his hair behind his ears, exposing the mark of his birth. 

On reflex, Seteth screwed his eyes shut, anticipating some sort of snide remark. 

Even though it was the professor. Even though it was Byleth, who had known the Immaculate One with far more intimacy than any of the Nabateans.

And even so, still, the professor could only speak her mind as she took him in fully for the first time.

“Seteth-,” Byleth breathed, “you’re-,”

The rest of her sentence died on her tongue and she faltered, gasping as she was overcome by the next wave of heat.

“Profess-,”

Byleth gripped Seteth’s sleeves in her fists, sucking in an inhale between her teeth. Her expression was twisted with pain as she subdued the desire.

“_Seteth_-,” she said again, desperation colouring her tone as she gazed up at him, “you’re-, you’re so very _beautiful_.”

The adviser pinked, startled by her words. The comment had fallen so naturally from her lips, the need to tell him as such, overpowering her body’s claim.

Something about it, about Byleth’s innate desperation coupled with the desperation to let Seteth know of his beauty, was enough to have him twitching in his trousers.

“_Professor_-,” 

“_Seteth_-,” Byleth answered in kind, shuddering as the adviser made short work of her overcoat, “I-, you-, please, _Seteth_-,”

Without waiting for a response of any sort, the professor unlatched her belt, letting her dagger tumble to the floor, shortly followed by her boots. 

Seteth knelt before her, taking her foot in his hand to remove the piece of armour that sat right over her left knee. Byleth stared at him, startled by the motion; she hadn’t realised he’d known about her old injury.

It never had healed quite properly, leaving her with a limp when the soreness was simply too much. But she’d never spoken of it before.

“Set-,”

“Byleth,” he breathed, lowering the metal piece to the floor and slowly rising, trailing his hands up her sides, “you’ll tell me if you’re in pain-, won’t you?”

“I-, have not often admitted pain to anyone,” she offered, recalling how Jeralt had simply learnt to interpret her miniscule reactions in place of words.

It had always worked for the two of them, even if no one else. But here was Seteth, making an effort; he wanted her to feel comfortable with him. That alone, was motivation enough.

“I’ll-, do my best.”

“That’s all I ask,” Seteth reassured gently, pulling her against his chest as he undid the back clasps of her breastplate.

Byleth sighed once he stepped back to remove it completely, leaving her in only her dark blouse. 

“Are you-, alright?” Seteth asked carefully, “Have the flashes passed?”

Just as the professor was about to reply, she clenched her jaw and hissed, stumbling away from Seteth as another wave of desire washed over her.

“It-, appears not,” she spat out, wrapping her arms around herself.

Seteth approached her, pulling the professor close and setting his hand to the back of her head, holding her steady as he bent to kiss her. Byleth huffed desperately against his lips, opening hers to receive him.

As the adviser tasted her, Byleth moaned against his tongue, pitching her hips towards his, aching for friction. She clenched her fists in his sleeves, ducking away from his mouth to rest her forehead against his wide chest.

“Seteth-,” she whispered, “I need more.”

The adviser blinked, startled once again by her uncharacteristic straightforwardness. But he would not deny her, instead parting the professor’s hair from her neck so he could fit his mouth to her skin.

Byleth gasped at the feel of his tongue upon her, trembling as Seteth dug his teeth ever-so-lightly into the skin right above her hammering pulse.

“_Seteth-,_” the professor hissed, one hand fisting in his dark hair, “_more-, more-!_”

He drew back for a quick breath and Byleth parted from him to yank her blouse over her head, discarding it hurriedly before returning her hand to Seteth’s hair, urging him to resume his ministrations at her throat.

The adviser paused, yearning to drink in the sight of Professor Byleth Eisner, formerly the formidable Ashen Demon, half-bare in his bedchamber. But the professor didn’t seem keen on giving him a moment’s respite.

Seteth assumed there would be time to take in the view at a later point; he would not fight Byleth as she bared her white throat for him. 

The adviser took no time selecting an untouched patch of skin to suck, testing a rougher bite.

Byleth seemed aroused by it, throwing her free arm around him and clenching a fist in his cloak, desperate to mould her body against his. Seteth figured he had only himself to blame for riling her up; it was often assumed that the Nabateans were particularly sensitive around the pulse. At the revelation that Byleth herself did not seem immune, Seteth found he could only hum in delight.

Byleth released the grip she had on the adviser’s cloak only to slowly drop her hand and palm herself carefully through her trousers.

“Seteth,” she whispered, “Seteth-, _Seteth-,_”

To hear her gasping his name with such unadulterated _need_-, Seteth had to halt his movement to keep himself from biting the professor with any more ferocity; it would do neither of them any good if he sank his teeth into her and let her bleed out.

“Professor-,”

The rest of his sentence died on his tongue as Seteth pulled back and lowered his gaze, watching Byleth manoeuvre the meat of her palm between her legs.

“Come now, Professor,” Seteth murmured, taking her wrist and pulling her hand from its place against her trousers, “there’s no need for such savagery.”

“Seteth-,” Byleth groaned, “I-, I’m-,”

She was trembling before him and the adviser hurried to help her remove her trousers and hose. Byleth shoved his hands away and yanked her trousers down, stepping out of them and collapsing back atop Seteth’s bed.

He couldn’t help but stare as the professor pulled her legs to her chest, wrenching her hose down her thighs. Seteth stepped up to help her pull them over her knees, taking special care of her old wound as he did.

Byleth had already tossed her panties over the edge of the bed when Seteth returned his gaze to her. She was panting, curling up slowly in the centre of his bed, unwilling to give in to the desire pumping through her veins. 

For a long moment, Seteth couldn’t help but wonder how many nights Byleth had done the same thing, willing the heat to subside as she tried to balance her busy Academy life with her personal trouble.

“I’m sorry-,” Seteth breathed, setting a chilly hand against Byleth’s bare skin, “I should’ve realised that you’d be effected, Professor.”

Byleth sighed again and it was the sound of one who had accepted the circumstance of their birth.

“Seteth,” the professor said, and her voice was hoarse as she glanced at him over her shoulder, “I want you to mate with me.”

The adviser could only gaze down at Byleth. Here was one of his own kind, asking to engage in their basest and yet most vital ritual with him. How many years, decades, _centuries_ had he spent denying himself? How long had he dealt with his own heat, aching and alone? But, no longer.

“Byleth-,” he murmured, and her name was soft off his lips, “Byleth, nothing could bring me greater pleasure, than to do this with you.”

The professor nodded, rolling over to gaze up into Seteth’s face. He took in a slow inhale and bent to remove his boots. They were followed shortly by his cloak before he turned back to Byleth.

She lifted her hands—the slight tremble was the only evidence she was apprehensive—and she carefully went about undoing the buttons at Seteth’s collar as he settled upon the bed beside her.

The professor had worried about Seteth’s initial response to her forwardness but he seemed at ease as she undid his belt and parted his robe. With his chest exposed, Byleth ducked close to run the pads of her thumbs across his bare skin. Seteth preened at the attention, eager for contact even if he didn’t declare it aloud.

“You hide under these robes so often,” Byleth whispered as Seteth snaked out of them, “I’ve nearly forgotten what a beast you must be beneath them.”

At the comment, the adviser’s cock twitched in his trousers. He hadn’t expected Byleth to be so forthcoming but perhaps now, amid the ebb and flow of her heat, she wasn’t particularly concerned about her loose lips.

Seteth, for one, found it equal parts endearing and arousing, being able to experience the professor uncensored like this.

“Just _look_ at you,” Byleth breathed, drawing him back to the present with a wide caress across his breast, “so toned-! Knowing you look like this, how could you _possibly_ stand to slip into those robes every day-?”

Seteth pinked.

“I-, surely you do not think me so extraordinary-,” he murmured, amused.

Byleth hummed thoughtfully.

“I s’ppose I have no reason to complain-, even with those robes, you can’t keep your best quality hidden,” she reminded, digging her fingernails into his breasts at the mention, “you truly have no _idea_ how close to madness you’ve driven me these past few days-,”

Seteth choked on a gasp at Byleth’s attention.

“Professor-,” he hissed, “what do you-,”

“You’re always so immersed in your work,” she growled as she recalled, “you’re oblivious to how the others look at you-, it’s not fair-, that they can look upon you. I want you all for myself now.”

The adviser pressed closer to her, eager for more of Byleth’s rough touches; she had no trouble riling him up. Perhaps it was punishment for his earlier behaviour. Perhaps it was just the professor.

“Your prowess on the battlefield-, the tenderness you show Flayn-, the way you get so worked up when you write-, and how you’re always leaving your damn quills lying around-, you’re-, I _envy_ her, truly.”

“_Who_-?” Seteth whispered, his voice strained as Byleth kneaded her hands against his tender breasts.

But as her words registered, the adviser realised what she’d meant. She’d been talking about-, his-,

“I can’t imagine it,” the professor murmured, and she paused her movement to put a hand to Seteth’s cheek, re-tucking his dark hair behind his pointed ear, “how wonderful it must’ve been, to love and be loved by you.”

“Byleth-, I-, if you truly want-, if you want _me_-, and-, and _this_-, then we’d-, we’d be a family. You and I. And Flayn.”

“We could fish,” she whispered.

Seteth smiled gently at her and it hurt. But it was a good sort of hurt; the kind he’d yearned to return to for so long, to remember what it felt like to love someone so fully—so wholly—that his heart swelled enough to burst from his chest.

“Don’t cry,” said Byleth, thumbing at his cheek.

The adviser put his hand over hers, “These are tears of gladness, Professor.”

“Seteth,” she said, “while I’m still myself, please-, won’t you make love to me?”

“Byleth-,” he breathed, cupping her face and pressing a kiss to her forehead, “Byleth, I will never deny you.”

Once Seteth had found some suitable oil and dropped his trousers, he sank back down onto the edge of the bed, taking Byleth’s hand in his own.

“Byleth-,” he said, “I truly do care for you.”

“I know, Seteth.”

“I want this-, experience-, to be a positive one,” Seteth said quietly, “so, if at any point, you want to stop-,”

“Cichol.”

Seteth looked up into Byleth’s face. He hadn’t registered her calling him by his true name, but her tone was so serious that he had no choice but to straighten to attention. The professor was gazing at him, perhaps seeing into his very soul with those deep eyes of hers. She gave Seteth a soft smile, the smallest of encouragements.

“It’s okay,” she promised, “I trust you.”

Before he registered his movements, Seteth leant in and captured Byleth’s lips with his own. She welcomed him eagerly, moaning deliciously into his mouth as he deepened their kiss.

The professor didn’t fight as Seteth slowly claimed more of the space between them, his free hand cautiously mapping out her exposed skin as he tasted her. The adviser traced Byleth’s collarbone, moving to put a hand to the back of her neck as he kissed down her jaw.

When Seteth ducked to add another mark to Byleth’s growing collection around her pulse, he heard her chuckle into his hair, the sound breathy but satisfied.

“You’ll have to be the one to explain that,” the professor warned, “should anyone comment.”

Seteth hummed noncommittally; there was no need to worry about the future just yet. For the night—for just this _one night_—he allowed himself the pleasure of simply enjoying Byleth. There was no reason to fear for what was to come, not now, not yet.

“Seteth-,” Byleth gasped.

It wouldn’t do to worry about how their lives would change, now that they were bound together. It wouldn’t do to worry over how Flayn would react—would she accept Byleth into her life? Would she accuse Seteth of forgetting about the past? Would she fear she’d have to compete with the professor for Seteth’s attention?

Would-,

“_Seteth-, please-,_” Byleth choked out, her hands fisting in his dark hair, “you tease me too much-,”

The desperation in her voice broke Seteth’s concentration and he blinked, releasing her as soon as he realised what he’d done.

“Byleth, I-,”

The professor’s neck was marked to high heaven and back. The welts and bruises were already on the rise and Seteth didn’t miss the lingering impressions of his teeth around the rougher patches.

“I-,”

Byleth yanked him by the hair, crushing her lips to his in a hungry kiss. Their teeth clacked at the sudden contact and Seteth groaned into Byleth’s mouth as the professor adjusted on the bed, settling atop his thigh. Seteth could feel her wet and the thought of it—of _him _being the one responsible—was enough to have him half-hard beneath her.

“_Professor-,_” Seteth gasped as Byleth rutted against his hip, hands wandering across the wide expanse of his chest.

“Seteth-,” she answered, equally breathless, “_Seteth-,_”

Sensing that the professor was dipping into another wave of heat, Seteth cautiously manoeuvred her from her place atop his thigh, pressing her back against the duvet.

Byleth already had her legs spread by the time Seteth had lathered oil across his fingers and turned back towards her. The display was so utterly debauched. Seteth felt desire stir slowly in his belly, coiling up tightly right against his hip.

The sight of Byleth stretched out across his sheets, Seteth’s bruises perching at her collar like a set of expensive black pearls as her pussy twitched, so eager to be filled by him-, oh, it was nearly too much. Far too much too soon.

“By-, by the _Goddess_, Byleth-,” he choked out.

The professor’ breaths came out in staccato pants, her chest rising and falling rapidly as Seteth finally resettled between her legs, ghosting his fingertips around her entrance.

When the pad of his thumb graced her clit, Byleth twitched with a desperate keen.

“Please, Seteth-,” she whispered, cracking open one eye to squint up into his face as he hovered over her.

The adviser stroked her clit again and Byleth writhed beneath him as Seteth pinned her down with one hand at the hip. He dug his fingernails into her skin and she gasped deliciously at the sting of pain.

“_Seteth-,_” Byleth begged, jerking her free hip up in an attempt to get his fingers closer to her entrance, “I-,”

Seteth slipped a finger into her and the professor tossed her head back, eyes screwed shut in relief as he wasted no time pumping it in and out of her.

“More-,” she hissed, clenching her fists in the sheets, “I need more, Seteth-,”

The adviser obliged, crooking a second finger up into her cunt and Byleth let out a grateful sound.

“Yes-,” she breathed, nodding emphatically as Seteth methodically opened her up, “yes, Seteth-, that’s good, Seteth-,”

The professor eased back against the sheets as some of her tension faded. Seteth took some pride in that, knowing that somehow, he’d managed to calm her fear and replace it with honey-sweet pleasure.

When he pumped a third finger up into her, Byleth snaked out from beneath his grip at her hip so she could meet him properly on the next punch of his fingers.

“Professor-,” Seteth warned.

“It’s coming-,” was all Byleth had to say in response, “I can feel it-,”

Sensing he’d prepared her properly, Seteth slowly pulled his fingers from within her and the professor sat up, disbelieving.

“Set-,”

“Sh, sh-,” he cooed, fisting his wet hand around his cock and jerking himself slowly, “have patience, Professor.”

“Seteth, _please_-,” Byleth hissed, throwing her head back with minute annoyance, “why do you torture me so-?”

“That is not my intent,” Seteth reminded hoarsely as he watched her pussy clench around nothing.

“_Seteth-,_”

The adviser sighed and lifted his free hand to hoist one of Byleth’s legs up to her shoulder, prying her open from a delicious new angle.

“Hush now, Professor,” he ground out, “I will give you what you need.”

Byleth squirmed beneath him and the adviser lifted his messy hand to his mouth. The professor stared at him, eyes wide as saucers as Seteth slowly licked her slick from between his fingers.

“Set-, Seteth-,”

“Byleth,” he said, dropping his gaze back to her face as he lowered his hand, “it’s time to relax and behave yourself. Open up for me now-, I know you can, can’t you, Professor?”

Seteth lined himself up with her and put the tip of his cock to her entrance. As he pressed into her, Byleth let out a pleased gasp, overjoyed that relief from her heat—at _long last_—was in sight.

“I missed a spot,” Seteth murmured to himself.

Byleth blinked, dazed as he offered her his hand. Then, realising what he wanted, the professor slowly opened her mouth, welcoming Seteth’s fingers between her lips.

“Very good,” he praised softly.

If he’d been intending to say anything else, the words were lost in his low moan as Byleth tongued between his fingers, pulling back only to suck at the digits.

Her attention was so focused on Seteth’s hand that he had to look away from her, distracted by the way she was so diligent in her task; it was not unlike the focus she showed in Academy drills but to devote such attention to so lewd a task-,

Seteth had to think of something else. He certainly had to stop himself from picturing Byleth on her knees, beneath the cover of his office desk, mouthing desperately at his trousers from her place between his legs-,

“_Byleth_-,” he rasped out, shoving deeper into her than he’d wanted.

The professor arched beneath him as he pulled his hand from her mouth and she released a surprised yelp as Seteth finally sheathed himself within her completely.

“Seteth-,”

“No, Professor-,” he gasped, “say my _name_.”

Byleth’s eyes rolled, confusion clouding her face as she tried to decipher his desire. She’d just said his-,

Oh.

“_Please_, Byleth-,” said Seteth as he slowly drew back, leaving only the head of his cock within her.

“_Cichol,_” she breathed.

And Seteth let out a guttural moan, thrusting quick and rough back into her. Byleth choked on a sob as he drew back and shoved into her again. Though the pace Seteth set was a slow one, he made up for it with brutally deep thrusts; it was as though he wanted Byleth to know that there was no part of her that could be kept from him. And that thought alone, was electrifying.

“Again-,” Seteth begged, pulling Byleth back into the present.

“_Cichol_-,”

He keened again at the sound of it, so easily moved by his true name spilling from her lips.

“By-, Byleth-,” Seteth gasped, “Byleth, you’re-, simply too good-,”

The clench of her around his weeping cock was an astronomical improvement compared to his fist; to have the professor choking on his true name as he fucked her through her heat was better than anything Seteth could ever have imagined.

“Seteth-,” Byleth whispered, digging her fingernails into the bare skin at him arms, “_Seteth_, I’m-,”

The professor jerked her hips and Seteth realised her orgasm was close. Of course it was; she was defenceless beneath her heat and for Seteth to buck into her without reserve, there was no doubt she wouldn’t last long.

“It’s alright-,” he bit out, his own rhythm faltering as Byleth got more vocal, releasing desperate mewls.

“_Seteth_-!” the professor moaned, her breathing erratic as her orgasm hit and her pussy spasmed around his cock.

The adviser bit his lip so hard it bled as Byleth jerked her hips desperately against his, milking the flow of pleasure for all it was worth.

“_Professor-!_” Seteth choked out, burying himself deep inside Byleth as he spent himself.

He gazed down at her and Byleth was wracked with shivers as she came down off her pleasure high.

“Set-Seteth-,” she whispered, catching his hand as he went to pull himself from her depths, “not yet-,”

He blinked, startled, but didn’t fight her, even if he was losing feeling in his toes from the positioning.

“Byleth, I’m-, it was not my intention to-, spill-,”

“No,” she interrupted, squeezing his hand, “no, it was good. I like it, the way it feels.”

Seteth pinked; the professor was still catching him off-guard with her commentary. Byleth traced meaningless runes across Seteth’s thigh as he slowly softened inside her.

“Lay with me,” the professor whispered.

Seteth drew himself from her slowly and some part of him—a part of which he was _very_ ashamed—was fascinated by the way Byleth’s insides didn’t want to let him go, even now, even when he’d given his all to satiate her and her heat.

But he freed himself from her, closed her legs, and collapsed gracelessly at Byleth’s side. The professor pulled him to her, burying her nose between his breasts so she could inhale his soft sea-scent.

“Cichol,” she breathed, pulling back so she could gaze up into his face.

“Byleth,” he returned, lifting a hand to trail his fingers through her hair.

She yawned and settled back against him; there was no need for words. The two of them had beaten her heat and with it, satisfied themselves in the way only two creatures of the same sort could.

“Seteth,” she said, “I-, I’m grateful. That you-, assisted me during this-, during my heat.”

The adviser only hummed, acknowledging her in the quiet darkness. This thing between them, this unspeakably primeval ritual they’d taken part in together, existed only here and now, beneath the pale glow of the moon.

“I’m glad,” Byleth added after a moment, “that it was you. I s’ppose it could’ve been anyone, but-,”

“I thought it was hopeless,” said Seteth, startling the professor, “I doubted I would ever be granted the chance to mate with one of my own.”

“What about-,”

“She was different,” Seteth cut in, even though it hurt, “those were different times. It was before she’d-, before we’d-, before Cethleann. Sothis-, there could have been others. I had always imagined there being others. I didn’t-, I never considered-,”

He trailed off. Byleth embraced him, tracing soothing patterns across his broad back. She ran her fingertips over the scars that littered his skin. There were two prominent marks that skirted down either side of his spine, the only proof of what he’d been.

“Do you miss it?” Byleth asked.

After learning the truth, she’d suspected Seteth had adopted wyvern riding in an effort to continue to fly the skies; he could feel the wind through his hair and the caress of the clouds, just like when he’d been-,

“All the time,” he answered, though it was not cold, “but, Byleth-,”

“What is it?”

The professor released him so she could pull back and look into his face. Seteth was frowning, debating on what topic was suitable for post-coital cuddling.

There must’ve been something in Byleth’s expression, though, because Seteth spoke his mind:

“I-, believe I may have limited myself,” he said, “in all these years at Garreg Mach, perhaps-,”

“You think you’ve always had your power?” Byleth whispered, begin to wonder.

Seteth nodded slowly, cautiously, as though voicing any confirmation aloud would shatter his hopes.

“I had to hide it,” the adviser admitted, “for the sake of self-preservation. For Cethleann.”

Byleth pressed closer to him and planted a long kiss to his neck. Seteth tipped his head to the side so she had better access to his pulsepoint.

“Even this,” he breathed as Byleth mouthed at his throat, “such reminders slip through—ghosts of what I was.”

He might’ve lost the ability to transform—or believed he had—but traces of the truth still remained.

“Of what you _are_,” the professor corrected, and her breath was warm against his pointed ear.

Seteth hummed in agreement, pleased.

“I should bathe you.”

“Later,” Byleth murmured, “I want to stay here.”

The adviser chuckled softly, amused by the admission.

“I’ll not complain,” he said, “I’ve grown quite fond of you like this.”

“Pressed up against you like a young lover?”

Seteth laughed again.

“You _are_ a young lover.”

“So are you,” the professor shot back.

“Hah, it merely _looks_ that way, I assure you.”

Byleth snorted but didn’t argue with him. She closed her eyes and listened to the slow beat of Seteth’s heart. How lovely a sound…

***

…Sunlight was streaming through the window pane when Byleth blinked awake. Seteth had his arm slung over her, hair tied back haphazardly at the base of his neck.

Byleth poked his cheek. When he snorted in his sleep, she had to cup a hand over her mouth to prevent a giggle from escaping.

“You’re always so tense,” she breathed, brushing her thumb across his cheek, “it comes as quite a shock that you can still manage to look so peaceful like this.”

Seteth nosed his way into her hair and Byleth held him, tracing the marks of his wings.

“We’ll miss brunch at this rate,” the professor said into the air.

It wasn’t as though she minded; there was nowhere else she’d rather be.

“There is no need for concern,” Seteth reassured quietly against her shoulder, “I could always cook something.”

“_You_? _Really_?” Byleth said with a laugh.

“Flayn says I have been steadily improving,” he snapped back with mock-hurt.

The professor rolled her eyes, disbelieving. Seteth drew back to look into her face. He didn’t say anything, but Byleth got the distinct impression it was only because he was lost in thought, gazing at her. Perhaps he was thinking back to last night; not that Byleth could blame him.

“Does it happen to you too, Seteth?”

He blinked, drawn out of his reverie.

“Does what happen to me?”

“The heat,” said Byleth, dropping her gaze.

Seteth sighed and nodded, “Yes. Although, I have dealt with mine since time immemorial; I’ve had much more experience.”

“Is it always like this?” the professor asked, “Wild and-, and manic?”

“If you’re lucky.”

Byleth squinted up at him, trying to decide if he was joking or not. When it became clear he was not, she wrinkled her nose.

“I don’t mean to frighten you,” Seteth elaborated quietly, “but I feel it’s better to be caught in a desperate thrall than to let it pass by without any feeling at all.”

Byleth didn’t say anything. She had only recently been burdened with the heats; she hadn’t had to exist without a mate for years and years like Seteth had.

“I-, I don’t mean to come across as insensitive,” she said.

“I know,” Seteth answered, brushing her fringe back from her face, “but, Byleth, I would suffer it a thousand times more if it meant I would get to experience a heat with you, even just once.”

When the professor did not immediately respond, Seteth tipped his head to one side, ears twitching. He was immediately concerned that he had somehow overstepped. Given their previous endeavours, that seemed like an impossibility but he was never quite certain about things when it came to Byleth; he was still working on learning each of her tiny tells.

But Byleth’s cheeks filled with blush and she put a fist to her mouth, reflexively hiding her delight.

“You’re-, pretty sly for a Saint,” she hissed, averting her gaze.

“I speak only the truth, Professor.”

As if to somehow prove his point, Seteth pressed a kiss to Byleth’s forehead and she hummed, pleased.

“We should think about getting up,” she reminded.

“Perhaps we shall gather the students for breakfast,” Seteth agreed.

Byleth stifled a yawn as she sat up, rubbing sleep dust from one eye before getting to a stand and stretching.

“I’ll worry about _my_ children,” she said, “_you_ worry about _yours_. Don’t forget you need to tell Flayn about-,”

The professor trailed off and waved her hand between them. Seteth flinched; he’d allowed himself the pleasure of forgetting about the future last night. But now, in the present, time was marching on.

Byleth was already collecting her clothes and inspecting the wrinkles with distaste.

“Yes,” Seteth mused from his place in the bed, “I thought perhaps-, we could tell her together.”

Byleth threw a glance at him over her shoulder.

“What are you talking about, Seteth? Of course we’re telling her together. We’re a family after all, aren’t we?”

The adviser blinked. Byleth didn’t seem to think much of her words; from her perspective, they were already a family and so it was natural that they tell Flayn together.

A slow, relieved smile spread across Seteth’s face.

“Rise and shine now, Cichol-!” Byleth trilled as she clasped her breastplate in place, “The cubs are likely starving in the Hall and you _know_ I don’t need any inquiries about my mysterious absence last night.”

Seteth could do little more than gaze at her as she tossed his discarded garments in his hamper and traipsed over to his wardrobe to select new ones.

He wordlessly thanked Sothis for everything.

“Seteth-,” Byleth prodded again, offering him his circlet and smoothing his wild bedhead, “it’s time for us to go and see the others.”

_Us._

The two of them, together. 

Seteth had a family again. Still a small one, but a family nonetheless. One with Byleth and with Flayn. And, perhaps, the entirety of Byleth’s student body.

“A bigger family, then,” he amended quietly.

And that thought brought the widest smile to his lips.

**Author's Note:**

> im thirsty and writing a part two of this already,,, releasing on the 13th of sept assuming god doesnt smite me for my work against the church ;-)


End file.
